Experience gained in the production of power supplies shows that tantalum capacitors exhibit a high failure rate, where the tantalum capacitors were used as an energy reservoir to supply controlled pulses of current to a load. Production failures can occur at system level testing, where a failure can prove to be quite costly, with a loss of production, and significant man-hours lost to repair and replace costly system parts.
Failure modes of interest for tantalum capacitors are low impedance paths, or even short circuits, between the capacitor's anode and cathode. The root-cause of the tantalum capacitor failures was found to be the initial application of voltage and/or pulsed current supplied to and from the capacitors.
Although tantalum capacitor failure modes and the root cause of such failures are well known, the high failure rates associated with these components appear to be accepted in OEM industry. The trend in manufacturing has been the use of finer powders to make tantalum capacitors, driven by a demand for smaller components. industry's response has been to de-rate capacitors. Thus, for example, early Mil Spec standards de-rated capacitor voltages by 70%; more recently, however, the de-rating level has been more typically at 50%. See MIL-HDBK-217F Notice 2, which can be found at www.weibull.com/knowledge/milhdbk.htm.
Prior to the testing and conditioning work described herein, there appeared to be no method for testing and conditioning tantalum capacitors to achieve a more robust device, beyond than that acknowledged by capacitor manufacturers. Present design practice in using tantalum capacitors in circuit designs calls for high de-rating factors, minimum circuit impedance (limit peak currents), and accepted failure rates that are too high for critical system design rates.